Flex lead assembly having minimum and substantially constant friction and torque

ABSTRACT

A flex-lead arrangement for providing a plurality of circuits electrically connecting stationary and angularly displaceable components. The arrangement provides substantially constant and minimum levels of friction and torque and maintains these minimum levels through wide angular displacements.

United States Patent Inventor George A. Kirsch Little Falls, NJ. 860,340

Sept. 23, 1969 Aug. 24, 1971 The Bendix Corporation Appl. No. Filed Patented Assignee FLEX LEAD ASSEMBLY HAVING MINIMUM AND SUBSTANTIALLY CONSTANT FRICTION AND TORQUE 6 Claims, 10 Drawing Figs.

US. Cl 307/145 Int. Cl H011 39/00 Field of Search 307/147, 145; 3 17/122 [56] References Cited UNITED STATES PATENTS -349,7l5 9/l886 Higham 307/145 1,422,429 7/1922 Filkins 307/145 X FOREIGN PATENTS 1,132,231 6/1962 Germany 307/l45 Primary Examiner- Robert S. Macon Attorneys-Anthony F. Cuoco and Flame, Hartz, Smith and Thompson ABSTRACT: A flex-lead arrangement for providing a plurality of circuits electrically connecting stationary and angularly displaceable components. The arrangement provides substantially constant and minimum levels of friction and torque and maintains these minimum levels through wide angular displacements.

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INVENTOR. GEORGE ,4. K/RSCH BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to flex-lead arrangements for use in gyroscopes and other like instruments and, more particularly, to flex-lead arrangements of the type described having substantially constant and minimum friction and torque.

2. Description of the Prior Art It is necessary, in gyroscopes and other similar electromechanical devices, to conduct current through multiple circuits at varying locations from stationary to movable components utilizing sliprings for flex-lead devices. Flex-leads are superior to sliprings for small angular displacements in that they are noise free and generate less friction and torque. However, flex-lead arrangements heretofore used still generate enough friction and torque to deteriorate instrument accuracy and have other inherent disadvantages. For example, on previous arrangements solder joints at terminal ends of the leads changed the lead stiffness along the working length of the leads and disturbed the uniformity of temper throughout the flex-lead material. Also, the leads have been preshaped to crescent or s-shaped leads or watch spring type coils which are susceptible to oscillations for generating errors. Moreover, these arrangements have been limitedto small numbers of circuits to avoid prohibitive friction and torque, and operation is restricted to small angular displacements. Constantly changing instrumentation requires displacements approaching 190 and the design limitations of present arrangements are incompatible with this magnitude of displacement.

SUMMARY OF THE INVENTION This invention contemplates a flexlead arrangement including a spool mounted to a movable component of a gyro or other like instrument on the sensitive axis, and an outer drum surrounding the spool and concentric thereto, and mounted on adjacent stationary instrument structure. Ribbon type flexleads are disposed between the spool and the drum to form symmetrically opposed equally spaced loops. Rotation of the spool allows the loops to roll concurrently in the same direction about the drum, with the loops always remaining in the same position relative to one another. For a specific angular rotation of the spool, both loops rotate in the same direction with the spool through a specific smaller angle predetermined by the ratio of the spool, loop and drum diameters. This ratio remains constant and the total angle of operation is regulated by the location of the loop ends relative to the spool and drum.

One object of this invention is to provide a flex-lead arrangement having minimum friction and torque. I -u Another object of this invention is to provide the flexlead arrangement wherein the minimum friction and torque are substantially constant.

Another object of this invention is to provide the flex-lead arrangement free of solder joints along the working length of the lead for uniformity of stiffness and temper in the flex-lead material.

Another object of this invention is to provide a flex-lead arrangement having design characteristics compatible with relatively large angular displacements.

Another object of this invention is to arrange the flex-leads for substantially constant and minimum bending to increase the life and reliability of the leads.

Another object of this invention is to provide a flex-lead arrangement so that susceptibility to operating oscillations is minimized.

Another object of this invention is to arrange the flex-lead for a minimal change in geometry and opposing spring energy.

Another object of this invention is to provide a fhex-lead arrangement having multiple circuit capability yet minimum torque and friction levels.

Another object of this invention is to reduce the cost of flexlead arrangements by eliminating preshaped heat treated leads.

These and other objects and features of the invention are pointed out in the following description in terms of the embodiments thereof which are shown in the accompanying drawings. It is to be understood; however, that the drawings are for the purpose of illustration only and are not a definition of the limits of the invention, reference being had to the appended claims for this purpose.

DESCRIPTION OF THE DRAWINGS With reference to the drawings, wherein corresponding elements are designated by corresponding numerals:

FIG. 1A is a diagrammatic representation of a flex-lead arrangement according to the invention.

FIG. 1B is a free body diagram of the forces through a section of the flex-lead arranged as in FIG. 1A.

FIGS. 2A through 2C are diagrammatic representations showing the relative displacement of the flex-leads as the spool of the invention is rotated.

FIG. 3 is a sectioned end view showing a spool and drum assembly according to the invention, and further showing a three-tiered flex-lead arrangement including six independent circuits.

FIG. 4 is a top view of the flex-lead arrangement FIG. 3.

FIGS. 5A through 5C show an alternative six-circuit flexlead arrangement.

With reference to FIG. 1A, a spool 2 having an external periphery 2A is mounted to a movable component or pivot 3 of a gyro or other like instrument 5 on the sensitive axis thereof, and a drum 4 having an internal periphery 4A is mounted concentric to spool 2 on adjacent stationary structure of gyro 5.

A pair of very thin (0.0005 inches thick) metallic ribbons of electrically conductive material designated by the numerals 6 and 8, and known in the art and referred to as flex-leads, are soldered at their ends to terminals 10 and 12 on spool 2 and to terminals 14 and 16 on drum 4. One end of each of the leads wraps around external periphery 2A of spool 2 and the other end wraps around internal periphery 4A of drum 4.

Flex-leads 6 and 8 are arranged to form symmetrically opposed equally spaced semicircular loops 7 and 9 having imaginary centers x and y, respectively. Rotation of spool 2 results in both of the loops rolling concurrently in the same direction about the spool, and always remaining in the same relative position to one another,.with the centers at and y, of the loops always being opposite as shown in FIG. 1A.

The normal forces at the points A and B of the loops tangent to spool 2 and drum 4 are always directed through the center of the spool as shown in the free body diagram of FIG. 1B.

This feature of the invention is further brought out in FIGS. 2A, 2B and 2C wherein loop 7 of flex-lead 6 is shown in positions resulting from rotating spool 2 in counterclockwise and clockwise directions from a chosen normal position, with the normal forces always being directed through the center of spool 2. The corresponding loop displacement is designated as 0 and 0 in FIGS. 28 and 2C, respectively.

Analysis of the flex-lead arrangement of the present invention is simplified by considering the flex-leads shown in the drawings as three separate spring elements:

1. The semicircular loop section of the flex-leads;

2. The portion of the flex-leads wrapped around external periphery 2A of spool 2; and

3. The portion of the flex-leads wrapped around internal periphery 4A of drum 4.

when viewed in terms of spring energy, since the loops remain geometrically constant, the only imbalance is from the curved ends of the flex-leads wrapped around the peripheries 2A and 4A of spool 2 and drum 4, respectively. At a center position (FIG. 1A) the flex-lead ends have identical lengths and are mirror images about the centerline. This arrangement represents a balanced system, with any friction and torque being at a negligible level. Considering an individual flex-lead, when the balance is disturbed by rotating spool 2 in either the clockwise or counterclockwise direction, one end of thelead winds while the other end unwinds equal peripheral lengths on the drum and spool peripheries. The resulting torque due to the change of opposing spring energies always acts to return the lead to the center or neutral position. The total torque magnitude is the differential value of the torques of all ends of the flex-lead pairs in a particular arrangement.

FIGS. 3 and 4 show an application of the invention wherein six individual circuits are provided, with said six circuits being arranged into three tiers, each of which includes two circuits.

Thus, FIG. 3 shows spool 2 secured to pivot 3 so as to rotate therewith, with drum 4 surrounding spool 2, and secured by screws 22 to instrument structure 5. A first tier includes flexlead circuits 24 and 26, a second tier includes flex-lead circuits 28 and 30 and a third tier includes flex-lead circuits 32 and 34. As shown in FIG. 4, spool 2 carries slots 40, 42, 44,

46, 48 and 50 and drum 4 carries correspondingslots 52, 54,

56, 58, 60 and 62. Corresponding slots in the spool and drum are at the same depth with three separate slot depths being provided for appropriate separation of the tiers.

With reference to FIGS. 3 and 4, then, it will be seen that flex-lead circuit 24 is positioned in slots 50 and 56 of spool 2 and drum 4, respectively, and flex-lead circuit 26 is positioned in slots 40 and 62 of spool 2 and drum 4, respectively, with slots 40, 50, 56 and 62 being at a depth to provide flex-lead circuits 24 and 26 at a first level or tier. In a similar manner, flex-lead circuits 28 and 30 are positioned in slots 44 and 54 and slots 42 and 60, respectively with said slots 42, 44, 54 and 60 being at another higher depth to form a second tier and flex-lead circuits 32 and 34 are positioned in slots 46 and 52 and slots 48 and 58, with said slots 46, 48, 52 and 58 being at yet another highest depth to form a third tier.

It will now be clear that flex-lead arrangements may vary in accordance with the particular requirements involved and still be within the scope of the invention. Thus, in FIGS. A, 5B and 5C there is shown for purposes of illustration an alternate six-circuit arrangement wherein two tiers are provided with each tier including three flex-lead circuits. In FIG. 5A a first tier including circuits 61, 63 and 65 is shown and in FIG. 58 a second tier including circuits 66, 68 and 70 is shown. FIG. 5C shows the composite two tier arrangement with it' being understood that the flex-leads are positioned in slots of appropriate depth to provide tier separation as heretofore explained with reference to FIGS. 3 and 4.

Still other variations may be obtained by arranging groups of leads bent in the same direction and on the same tier balanced by an equal number of leads arranged in opposite directions on parallel tiers as illustrated in the figures. If a particular application requires that an odd number of circuits be provided, a torque and friction level will result because of the geometric unbalance. However, this level will still be a fraction of that occurring if brushes or sliprings or conventional flex-lead arrangements are used, and thus the invention still represents a distinct advantage over flex-lead arrangements now known in the art.

It will now be seen from the aforegoing description of the invention that there is provided a flex-lead arrangement having relatively low and substantially constant bending stress to assure high reliability and life. A minimal change in both the geometry of the parts and the level of spring energy is achieved as well as increased stability under conditions of vibration. Uniformity of temper throughout the flex-lead material is achieved by elimination of solder joints along the working length of the flex-lead. Since all normal forces within the flex-lead are directed through the center axis of the spool,

torques due to these components are negated. Electrical noise such as may' occur when sliprings are used is eliminated and since the flex-leads may come from a spool or ribbon of appropriate material, preshaped and heat-treated individual flexlead forms are eliminated to over flex-lead arrangements now known in the art.

While several em odiments of the invention have been illusthose skilled in the art may be made without departing from the scope of the invention. Reference is, therefore, to be had to the appended claims for a definition of the limits of the invention.

lclaim:

1. A circuit arrangement for conducting current between stationary and rotatable instrument components, comprising:

a spool mounted to the rotatable instrument component for rotating therewith; a'drum surrounding the spool and concentric thereto, and

- mounted on adjacent stationary instrument structure; a plurality of flex-leads arranged in a plurality of tiers, each tier including a plurality of flex-leads having ends secured to the spool and drum and disposed therebetween for forming pairs of symmetrically opposed equally spaced loops, with the loops rolling concurrently in the same direction as the spoolabout the drum and always remaining in the same position relative to one another.

2. A circuit arrangement as described by claim I, wherein:

the spool. and drum carry corresponding slots at various depths around the circumferences thereof for supporting the flex-leads to provide tier separation.

3. A circuit arrangement as described by claim 1, wherein the plurality of flex-leads arranged in a plurality of tiers includes:

six flex-leads arranged into three tiers, each of which includes two flex-leads formed to provide a pair of equally spaced symmetrically opposed loops.

4. A circuit arrangement as described by claim 1, wherein the plurality of flex-leads arranged in a plurality of tiers, in-.

cludes:

, first and second tiers;

the first tier includes three flex-leads formed in one direction to provide three equally spaced loops; and

the second tier includes three flex-leads formed in the opposite direction to provide three equally spaced loops for balancing the loops in the first tier.

5. A circuit arrangement as described by claim 1, wherein the plurality of flex-leads arranged in a plurality of tiers includes:

an even number of flex-leads arranged in a plurality of parallel tiers, with the flex-leads formed so that each tier provide a distinct cost advantage 

1. A circuit arrangement for conducting current between stationary and rotatable instrument components, comprising: a spool mounted to the rotatable instrument component for rotating therewith; a drum surrounding the spool and concentric thereto, and mounted on adjacent stationary instrument structure; a plurality of flex-leads arranged in a plurality of tiers, each tier including a plurality of flex-leads having ends secured to the spool and drum and disposed therebetween for forming pairs of symmetrically opposed equally spaced loops, with the loops rolling concurrently in the same direction as the spool about the drum and always remaining in the same position relative to one another.
 2. A circuit arrangement as described by claim 1, wherein: the spool and drum carry corresponding slots at various depths around the circumferences thereof for supporting the flex-leads to provide tier separation.
 3. A circuit arrangement as described by claim 1, wherein the plurality of flex-leads arranged in a plurality of tiers includes: six flex-leads arranged into three tiers, each of which includes two flex-leads formed to provide a pair of equally spaced symmetrically opposed loops.
 4. A circuit arrangement as described by claim 1, wherein the plurality of flex-leads arranged in a plurality of tiers, includes: first and second tiers; the first tier includes three flex-leads formed in one direction to provide three equally spaced loops; and the second tier includes three flex-leads formed in the opposite direction to provide three equally spaced loops for balancing the loops in the first tier.
 5. A circuit arrangement as described by claim 1, wherein the plurality of flex-leads arranged in a plurality of tiers includes: an even number of flex-leads arranged in a plurality of parallel tiers, with the flex-leads formed so that each tier includes a pair of symmetrically opposed equally spaced loops.
 6. A circuit arrangement as described by claim 1, wherein the plurality of flex-leads arranged in a plurality of tiers includes: a first tier having an odd number of flex-leads formed in one direction to provide a corresponding odd number of equally spaced loops; and a second tier having the same number of flex-leads formed in the opposite direction to provide the same number of equally spaced loops for balancing the loops in the first tier. 